MPG tune-up for 289. What cam? Best carb? Any other bolt-ons?

[Greg Bell]

Hey guys,

I know some folks find this topic annoying, but I really think a 2-4 mpg improvement in fuel usage is worth the hassle. I have a 67 Bronco that I intend to be my daily driver. Now, I currently drive a Chevy 1500 extended cab and it gets about 14mpg (160k, automatic). If I can match it then I am happy.

This is not a highway truck. My wife has a Honda Fit and all our extended trips are in it. So I am not sure if I should replace my 3 speed.

It is my understanding that my transmission and driveline is basically stock except for disk brakes up front. Obviously, the tires are oversized.

So, given a pretty stock 289 and 3 speed, what should I do.

I hate to admit it, but I really don't know what kind of lift I have (I see a lot of Duff stuff under there), but it looks to be at least 2-3 inches. I like the way the Bronco looks, and I am getting it painted after I get the AC installed and the power steering pump and E-brake fixed (in the shop now).

So, right now, what should I do to get my MPG from about 10 (almost all city) to 14-15?

1. It has some sort of Edlebrock carb and I suspect the prior owner had it tuned for awesomeness rather than MPG. The engine sounds very meaty. Should I bother replacing this or should a competent shop be able to tune this for MPG? It has electronic ignition.

2. I have no idea what kind of cam it has. It isn't peaky so I suspect it is stock or mild. Is there a better cam for MPG?

3. Should the gearing be changed? What exactly would be involved in this?


4. I am not an aggressive driver. Frankly, I don't think the 10mpg I am getting now is that bad considering it is a very heavy 4 wd and big tires. But 4 mpg would probably put $600 per year back in my pocket, so it seems worthwhile to look into.

 

[jdcone]

Tear out the seats, windshield, transfer case, front drieshaft, and anything else that has ANY weight to it. 10mpg? That's actually pretty good for a non-efi V8 brick on wheels. Having a manual trans is better than an auto. Putting EFI in will help a lot.

 

[Greg Bell]

The engine seems very strong and I know the heads were redone in the last 5k or so. Any recommendations on the EFI?

 

[av bronco]

I would go Ford EEC IV efi, you can get a custom harness made for a bronco, and shop around for computer, intake, ect. heres a link.
http://www.bcbroncos.com/fuelefi.html

 

[broncnaz]

Well thats a loaded question as city driving your just not going to improve mileage a whole lot. But tuning can help a little.

I'm going to disagree with the two answers you've gotten so far. EFI wont gain much if any mileage over a properly tuned carb and you really cant remove enough wieght from a bronco that will be of any help you still have to push a box through the air. Stop and go driving is your problem.

Need more info what axle gearing do you have and what tire size? Are you running headers? Whats the timing set at? What color are the sprak plugs? Then we can make some better suggestions.

It would be nice to know what size cam shaft you have but it may be a typical low rpm type cam. you could install a vacuum guage see what readings you get a idle and at cruise RPM that would tell you/us quite a bit. Camshaft is probably the most critical item in gaining mileage as it should be matched to your overall gearing and driving needs.

As for your carb check your jetting if the plugs are black then it can be leaned out. if they are white it needs to be richened up. both cause mileage losses. I would suggest you get a tuning kit for the carb and do the work your self if you take it to a shop I really doubt they will do much for you other than relieve you of some cash.

Igintion timing can help mileage as well you should be able to run 10-12 degrees intial timing and get a slight improvement in power and mileage. Also your advance curve should be set so it all come in by 3000 rpm.

It all depends on total setup and proper tuning. With my 73 I get 16 mpg on the hiway at 65mph. 17 mpg when the wind is blowing right. In the city it gets about 12-13 if I'm lucky.

 

[Greg Bell]

Tire size I can get. How do I determine my axel gearing? What is the preferred gearing?

What is the best cam for this application?

Thank for the advice on the carb tuning. I will take that route.

If I can get to 12-13 it will be worth it. Especially if all that is needed is carb tuning. Heck, $600 a year covers a lot of tuning.

 

[broncnaz]

Prefered gearing depends on tire size. There a re few ways to determine gearing one is check the code on the VIN tag, next check the axle housing for a small metal tag it will have gear ratio stamped into it. sometimes those tags are long gone. they lastly you can jack up the rear end and count driveshaft revolutions while some one turns the tire one full turn. but thats a little more involved.

Again camshaft really depens on gearing tire size and intended useage. Usually something like a edelbrock perfromer cam is a good choice.
I would think that if your tire size and gearing are not to far off and the engine is tuned good you should be able to get about close to 15 on the hiway but still city driving is not good for mileage so if you get 12-13 I would say you'd be doing great.